1. Field of the Invention
This invention relates to an exhaust system especially for a tool driven by pneumatic pressure which causes exhaust discharged not from the tool but from the driving air supply source. More specifically, this invention relates to air supply and an exhaust system for pneumatic tools and particularly to an air supply and exhaust system which does not only reduce exhaust noise of a pneumatic tool but prevent the dust scattered by an exhaust air flow from scattering.
2. Description of the Related Art
Tools driven by pneumatic pressure, hereinafter simply called as pneumatic tools or tools, are normally arranged so that the compressed air used to drive the tools is discharged from exhaust ports into the atmosphere. However, the exhaust contains oil content and dust such as sealant dust discharged from the tool and it is undesirable that the oil content and dust are discharged into the atmosphere in view of the preservation of the environment. Moreover, because in these kind of tools, especially nailing machines, compressed air used to drive striking pistons is rapidly discharged from exhaust ports, expansion of compressed air, generation of whirling flow cause and the like cause noises. In addition, exhaust flows of compressed air blow around and diffuse dust and the like.
In view of the above, conventionally, filters are installed in the exhaust ports of the pneumatic tools so as to remove oil content, sealant dust and the like and to reduce noises by suppressing the rapid expansion of exhaust air.
However, such an arrangement for exhausting air through a filter as mentioned above may only result in decreasing output power of the tool if the flow rate of exhaust air is suppressed by the filter. Therefore, control of the flow rate of exhaust air needs to be eased, but sufficient noise reduction is not achieved.
Increasing the area of the opening of such a filter can be reasoned to cope with the problem mentioned above. This may achieve effect of the noise reduction without lowering the performance of the tool. However, the problem is that the shape and weight of the tool tend to increase, and this will result in reducing the workability.
In another conventional system for a pneumatic tool, the exhaust air is guided through an exhaust hose other than a supply hose so as to exhaust air from the tool. Then, the exhaust air is emitted into the atmosphere through an exhaust purifier having a built-in filter for soundproofing and dust-removing which is provided in the end portion of the exhaust hose.
However, in the conventional systems, two hoses have to be connected to the tool, so it results in spoiling the workability because the steering of the tool and the like become troublesome. Moreover, the laborious task of handling the tool ensues because it is necessitated to not only install the exhaust purifier separately but also move a compressed air supply source such as a compressor and the exhaust purifier when the work place is changed.
Tools such as nailing and staple driving machines driven by pneumatic pressure are constructed so that an exhaust port is provided in the head portion of a housing incorporating a pneumatic cylinder for driving a driver. The tools are also constructed so that a piston returns to a standby position by discharging pressurized air in the back of the piston from the exhaust port into the atmosphere after a nail or a staple is driven in. Therefore, the sound pressure felt by an operator is high because the pressurized air is discharged in the proximity of the operator holding the pneumatic tool. This results in accelerating operator's tired feeling to the extent that cannot be neglected. There are other problems arising from deteriorating working environment such as dust, sawdust and the like are blown up by the air flow jetted out of the exhaust port.
In order to solve the foregoing problems, there has been proposed an arrangement in which a pipe joint between a pneumatic tool and an air hose is built in the form of a coaxial double pipe comprising a center passage as an air supply passage and an outer passage as an exhaust passage surrounding the center passage (Japanese Utility Model Application Laid-open Sho. 50-27608).
In the case of the pipe joint mentioned above, pressurized air is supplied from an air compressor through the center passage of the pipe joint to the air chamber of the pneumatic tool, and exhaust is discharged through the outer passage after the air is used to drive an air cylinder. In other words, the air hose connected through the pipe joint to the pneumatic tool has of coaxial double tubular construction. That is, an outer hose is provided on the outer periphery of an air supply hose up to certain length from the pipe joint, and the end portion of the outer hose is left open as the outer hose ends in the middle of the coaxial air hose. Consequently, the exhaust air after driving the pneumatic cylinder is discharged into the atmosphere from the open end portion of the outer hose through the outer passage of the pipe joint and the outer hose of the coaxial air hose.
When the pipe joint and the coaxial air hose are employed, an exhaust port is placed away from an operator by the coaxial air hose with the effect of reducing the noise felt by the operator and preventing dust and the like from being blown up against the face of the operator. However, the absolute volume of the exhaust sound even in this case is not much different from one in the type in which the air is directly exhausted from the pneumatic tool since this case is less effective in terms of reducing the exhaust sound. On the contrary, when the coaxial air hose is moved around on the floor surface, the amount of dust and the like scattered may become greater than the amount of dust and the like directly exhausted from the pneumatic tool because the exhaust from the exhaust port in the end portion of the outer hose is in contact with the floor surface.